A test apparatus for testing the operation of a lighting system is disclosed in U.S. Pat. No. 6,542,082, which discloses determination of whether a lighting device in a group of lighting devices contained in a remotely located unit under test works properly or not. The determination is done by selecting one lighting device at a time and testing that lighting device. Thus, the test apparatus transmits control signals to the unit under test for selecting a lighting device and for changing the operational state of the selected lighting device, and determines a change in the current that is drawn by the unit under test. For example, if the test apparatus determines that there is no change of current or if the change is less than expected, then it decides that the lighting device is defective.
Such an individualized testing is possible in lighting systems where an individual lighting device can be identified. However, such lighting systems are undesirably expensive for many applications. Therefore, it would be desired to be able to remotely detect defective lighting devices also in less expensive lighting systems where it is not possible to select and identify an individual lighting device.